In many computer systems multiple integrated circuit chips communicate with each other to perform the programmed operations. The different chips may include central processing units, high speed memories, mass storage devices, chipsets, video processors, and input/output interfaces. Some computers may have more than one of each of these kinds of chips. The chips are traditionally mounted to a motherboard or system board either directly or through a socket or a daughter card.
The chips traditionally communicate using copper interconnects or links that travel through the chip's package vias, through the socket, through the platform motherboard and then back through the socket (or other interconnect) and package of the next chip. In another variation, a flexible connector cable is connected directly between two different packages to bypass the socket and the platform motherboard. This provides a more direct path with fewer interfaces through different connections.
For high performance computing and server platforms the speed of communication between the chip packages and other peripheral or parallel computing systems may limit the overall system performance. The socket, traditionally used to connect chips to a motherboard or system board, has a limited data rate due to the many interfaces for a signal to travel from one chip to the next through a package, the socket, the system board and up through another socket to the other chip. For servers connected through a server backplane, a signal may travel from one chip to another server through a package, the socket, the system board and then to a server backplane or through the motherboard to the backplane. There are additional signal interfaces to connect from the server backplane to the signal's destination. These data signal lines also require physical space in the socket and in the system board.
Flex cables with multiple parallel conductors are used to conduct data signals over short distances between CPUs or between a CPU and another component. The flex cable is attached directly to the chip packages after the chips are socketed in the system board. The package substrate has a cable connector on one or more edges and a cable is attached to each connector. The cable connects two different chip packages together or to a server backplane. This avoids routing the signal through the socket. For longer distances, optical interconnects are expected to be used. In the same way, the package is first socketed to the system board. The package includes an optical fiber connector on the edge of the package substrate and the optical fibers are connected directly to the package substrate.